Probabilistic power indices for games with abstention∗

In this paper we introduce eight power indices that admit a probabilistic interpretation for voting rules with abstention or with three levels of approval in the input, briefly (3,2) games. We analyze the analogies and discrepancies between standard known indices for simple games and the proposed extensions for this more general context. A remarkable difference is that for (3,2) games the proposed extensions of the Banzhaf index, Coleman index to prevent action and Coleman index to initiate action become non–proportional notions, contrarily to what succeeds for simple games. We conclude the work by providing procedures based on generating functions for (3,2) games, and extensible to (j,k) games, to efficiently compute them.